Coronary artery disease remains the leading cause of morbidity and mortality in Western societies. Coronary artery disease is manifested in a number of ways. For example, disease of the coronary arteries can lead to insufficient blood flow to various areas of the heart. This can lead to the discomfort of angina and the risk of ischemia. In severe cases, acute blockage of coronary blood flow can result in irreversible damage to the myocardial tissue including myocardial infarction and the risk of death.
A number of approaches have been developed for treating coronary artery disease. In less severe cases, it is often sufficient to merely treat the symptoms, with pharmaceuticals, or treat the underlying causes of the disease, with lifestyle modification. In more severe cases, the coronary blockage can be treated endovascularly or percutaneously using techniques such as balloon angioplasty, atherectomy, laser ablation, stents, and the like.
In cases where these approaches have failed or are likely to fail, an alternative is to perform a coronary artery bypass graft (CABG) procedure. CABG surgery, also known as “heart bypass” surgery, generally entails the use of a graft or conduit to bypass the coronary obstruction and, thereby provide blood flow to the downstream ischemic heart tissues. The procedure is generally lengthy, traumatic and subject to patient risk. Among the risk factors involved is the use of a cardiopulmonary bypass (CPB) circuit, also known as a “heart-lung machine”, to both pump blood and oxygenate the blood so that the patient's heart may be stopped during the surgery, with its function performed by the CPB circuit.
Conventional CABG procedures are typically conducted on an arrested heart while the patient is on CPB. The CPB circuit provides continuous systemic blood circulation, while cardioplegic cardiac arrest enables meticulous anastomosis suturing in a bloodless, still operative field. In the majority of patients, obstructed coronary arteries are bypassed; for example, with an in situ internal mammary artery (IMA) or a reversed segment of saphenous vein harvested from a leg.
Segments of other suitable blood vessels may also be used for grafting depending on availability, size and quality. In general, the body hosts seven potential arterial conduits, the right and left IMAs, the radial arteries and three viceral arteries, one in the abdomen, and two in the lower abdominal wall, though the latter may be quite short and are generally of limited usefulness. The viceral arteries include the gastroepiploic artery and the splenic artery.
The left IMA is best used for bypass to the left anterior descending (LAD) coronary artery and its diagonal branches. Whereas, the right IMA may be used for bypass to selected vessels more posterior such as the distal right coronary artery (RCA). The right IMA may also be used for bypass to selected marginal branches of the left circumflex coronary artery. A segment of radial artery harvested from an arm is generally used to revascularize the posterior surface of the heart. The right gastroepiploic artery may be used to revascularize almost any artery on the surface of the heart. It is most commonly used for bypass to the distal RCA or the posterior descending coronary artery. In unusual circumstances the splenic artery is used to revascularize posterior coronary arteries, but it is long enough to reach the marginal branches of the circumflex coronary artery.
Surgeons will generally complete bypass grafts to the following coronary arteries in a patient undergoing multiple bypass surgery in roughly the following order: posterior descending coronary artery (PDA), RCA, obtuse marginal branch, circumflex coronary artery, diagonal branch, and LAD. More generally, surgeons will revascularize the three coronary systems in the following order: right, circumflex, and anterior descending. However, the order may vary depending on whether the procedure is performed on a beating heart or an arrested heart. For arrested heart, about 3 to 4 bypass grafts of which 1 to 3 are free grafts are generally performed per procedure. In contrast, about 2 to 3 bypass grafts of which 0 to 2 are free grafts are generally performed per beating heart procedure. In general, 1 free graft is used per beating heart procedure.
When a saphenous vein or other blood vessel is used as a free graft in a procedure, two anastomoses are performed; one to the diseased artery distal to the obstruction (outflow end), and one proximally to the blood vessel supplying the arterial blood (inflow end). These anastomoses are generally performed using end-to-side anastomotic techniques. Rarely an end-to-end anastomotic technique is used. When more than one graft is required in any of the three coronary systems for complete revascularization of the heart, sequential graft techniques may be used to conserve the amount of blood vessels required. Sequential graft techniques use proximal side-to-side anastomoses and an end-to-side anastomosis to complete the graft. For example, a common sequence used in the anterior descending coronary system is a side-to-side anastomosis of graft to the diagonal branch and an end-to-side anastomosis of graft to the LAD coronary artery. However, only a small percentage of anastomoses are side-to-side anastomoses.
The majority of surgeons will complete the distal anastomosis of a graft prior to completion of the proximal anastomosis. The small percentage of surgeons who do complete the proximal anastomosis first usually do so to allow antegrade perfusion of cardioplegic solution through the graft during revascularization. Construction of the distal anastomosis, e.g., a saphenous vein-coronary artery anastomosis, begins by first locating the target artery on the heart. Next, an incision is made through the epicardium and the myocardium to expose the artery. An arteriotomy is then made using a knife to incise the artery. The incision is then extended with a scissors. The length of the incision approximates the diameter of the saphenous vein, about 4 to 5 mm. The diameter of the target artery is generally 1.5 to 2.0 mm. Since, most surgeons currently feel the distal take-off angle should be 30 to 45 degrees, the distal end of the saphenous vein is usually beveled at about 30 to 45 degrees.
Currently, surgeons generally construct the anastomosis via a ten-stitch running suture using 7-0 polypropylene suture material. The ten-stitch anastomosis typically comprises five stitches around the heel of the graft and five stitches around the toe. The five stitches around the heel of the graft comprise two stitches to one side of the apex of the graft and the artery, a stitch through the apex and two stitches placed at the opposite side of the apex. The graft is generally held apart from the coronary artery while the stitches are constructed using a needle manipulated by a forceps. Suture loops are drawn up and the suture pulled straight through to eliminate purse-string effect. The five stitches around the toe of the graft also comprise two stitches to one side of the apex of the graft and the artery, a stitch through the apex and two stitches placed at the opposite side of the apex. Again, suture loops are drawn up and the suture pulled straight through to eliminate purse-string effect. The suture ends are then tied.
The proximal anastomosis of a saphenous vein graft to the aorta, i.e. an aortosaphenous vein anastomosis, is formed by first removing the pericardial layer that covers the aorta. An occluding or side-biting clamp may be placed on the aorta at the anastomosis site or an aortotomy occlusion device may be used following creation of the aortotomy. A small circular or elliptical portion of the ascending aorta is excised forming a small opening 4 to 5 mm in diameter, i.e. the aortotomy. An aortic punch typically facilitates this procedure. The opening for a right-sided graft is made anterior or to the right lateral side of the aorta, whereas an opening for a left-sided graft is made to the left lateral side of the aorta. If the graft is to supply blood to the right coronary artery, the opening is generally made proximal on the aorta. If the graft is to supply blood to the anterior descending coronary artery, the opening is generally made in the middle on the aorta. And, if the graft is to supply blood to the circumflex artery, the opening is generally made distal on the aorta. The right graft opening is placed slightly in the right of the anterior midpoint of the aorta and the left graft opening slightly to the left. The end of the saphenous vein is cut back longitudinally for a distance of approximately 1 cm. A vascular clamp is placed across the tip of the saphenous vein to flatten it, thereby exposing the apex of the vein. Five suture loops of a running suture using 5-0 polypropylene are then placed around the ‘heel’ of the graft and passed through the aortic wall. Two stitches are placed on one side of the apex, the third stitch is placed precisely through the apex of the incision in the saphenous vein, and the final two stitches are placed on the opposite side of the apex. Suture traction is used to help expose the edge of the aortic opening to ensure accurate needle placement. Stitches include about 3 to 5 mm of the aortic wall for adequate strength. Suture loops are then pulled up to approximate the vein graft to the aorta. The remaining stitches are placed in a cartwheel fashion around the aortic opening thereby completing the remainder of the anastomosis.
Left-sided grafts are oriented so the apex of the incision in the “heel” of the saphenous vein will face directly to the left side. The stitches are placed in a clockwise fashion around the heel of the graft and in a counterclockwise fashion around the aortic opening. Right-sided grafts are oriented in a caudal fashion. The stitches are placed in a counterclockwise fashion around the heel of the graft and in a clockwise fashion around the aortic opening. Five suture loops complete the heel portion of the graft and an additional five or six may be used to complete the toe of the graft. Finished proximal anastomoses typically have a “cobra-head” appearance.
The surgeon takes steps to minimize the possibility of thrombosis, narrowing and/or premature closure of the anastomosis due to technical errors. Some surgeons feel the proximal anastomosis must have a take-off angle of 45 degrees while other surgeons believe the take-off angle is not critical. In addition, it was felt that intima-to-intima contact of the vessels at the anastomosis was critical for endothelization to occur, thereby making an ideal union of the vessels. However, most surgeons now feel intima-to-adventitia contact is acceptable. The main objective of the surgeon is to create an anastomosis with an expected long-term patency rate of greater than 5 to 10 years. The creation of an anastomosis currently takes approximately 10-15 minutes.
An important consideration for creating an anastomosis without error is adequate exposure of the target vessel. Acute visualization of the vessel walls is mandatory in order to properly place each stitch and avoid inadvertently including the back wall of the vessel in a stitch, which in effect narrows or completely occludes the vessel. In order to achieve the required exposure most surgeons will employee blood-less field devices such as shunts, snares, and misted blowers. Further, largely invasive surgical techniques are also employed to help the surgeon gain access to the grafting site. For this reason, CABG surgery is typically performed through a median sternotomy, which provides access to the heart and to all major coronary branches. A median sternotomy incision begins just below the sternal notch and extends slightly below the xiphoid process. A sternal retractor is used to spread the left and right rib cage apart for optimal exposure of the heart. Hemostasis of the sternal edges is typically obtained using electrocautery with a ball-tip electrode and a thin layer of bone wax. The pericardial sac is opened thereby achieving direct access to the heart.
A blood vessel or vessels for use in the graft procedure are mobilized from the patient. This usually entails mobilizing either a mammary artery or a saphenous vein, although other graft vessels as discussed above may also be used. A heart-lung or cardiopulmonary bypass is performed. This usually entails arterial and venous cannulation, connecting the bloodstream to a heart-lung machine, cooling the body to about 32 degrees Celsius, cross clamping of the aorta and cardioplegic perfusion of the coronary arteries to arrest and cool the heart to about 4 degrees Celsius. A proximal anastomosis may be performed on partial bypass using a partial occluding aortic cross-clamp or side-clamp. The arrest or stoppage of the heart is generally required because the constant pumping motion of the beating heart would make surgery upon the heart difficult in some locations and extremely difficult if not impossible in other locations
Once cardiac arrest is achieved, then a graft (or grafts) is attached to the relevant portions of a coronary artery (or arteries) followed by weaning from the cardiopulmonary bypass, restarting the heart and decannulation. Finally the chest is closed.
Problems that may be associated with conventional CABG procedures with CPB include the initiation of a systemic inflammatory response due to the interactions of blood elements with the artificial material surfaces of the CPB circuit. Global (hypothermic) cardiac arrest may result in global myocardial ischemia and cross clamping the ascending aorta may contribute to the patient experiencing a post-operative stroke. In fact, recent studies have shown aortic clamping and manipulation may release atherosclerotic debris into the bloodstream, resulting in neurologic injury.
Currently, the golden standard for creation of a vascular anastomosis is manual suturing. Manual suturing may be used to attach vascular grafts (either autografts or prosthetic grafts) for coronary bypass, femoral-femoral bypass (to relieve inadequate circulation in the legs), and AV fistulas and/or shunts (access portals for repeated puncture applications such as kidney dialysis or diabetes). However, a number of cardiac surgical procedures, e.g., off-pump, beating heart CABG procedures, minimally invasive procedures and even totally endoscopic procedures with access through ports only, may require a variety of new anastomotic techniques. The ability of performing anastomoses with limited or no CPB support may increase the possibility of performing more CABG procedures using minimally invasive surgical techniques. Avoiding the use of cross clamps and CPB or dramatically reducing pump run and cross clamp times may effectively minimize post-operative complications. For this reason, there is an increasing need for easier, quicker, less damaging, but reliable automated, semi-automated, or at least facilitated methods to replace or enhance the normal process of a manually sutured vascular anastomosis.
The major objective of any CABG procedure is to perform a technically perfect anastomosis. However, creation of a technically perfect anastomosis is generally complex, tedious, time consuming and its success is highly dependent on a surgeon's skill level. Therefore, creation of vascular anastomoses without the need to perform delicate and intricate suture lines may enable surgeons to more quickly create simpler and effective anastomoses. Currently, there are a number of techniques or procedures being investigated for facilitating the process of forming an anastomosis including vascular clips or staplers, glues, adhesives or sealants, laser welding, mechanical couplers, stents and robot-assisted suturing. These techniques are being developed for performing end-to-end, end-to-side and/or side-to-side anastomoses with or without temporary blood flow interruption. In general, these techniques may include the use of various biomaterials and/or biocompatible agents.
In an effort to reduce or eliminate occlusive anastomosis time, various techniques or procedures are being investigated. These procedures include coronary shunting techniques, which enable manual suturing without time-constraint due to persistent distal perfusion, and accelerated tissue-bonding techniques, e.g., tissue adhesives and laser welding. Some nonocclusive anastomosis techniques being developed require apposition of the intima of the graft to the adventitia of the recipient artery.
Sealants, adhesives or glues may be based on synthetic or biological substances or a combination of both. They are generally used to either seal post-operative internal air or fluid leaks, or to close a topical wound. Surgical sealants are generally absorbable materials used primarily to control internal bleeding and to seal tissue. Surgical adhesives, stronger than sealants, are often non-absorbable, but tend to be biologically based. Surgical glues, stronger than adhesives, are often synthetic and non-absorbable. In addition, glues are often used for topical wounds. Surgical glues are typically made from cyanoacrylates, a strong adhesive found in commercially available super glues. Biologically based sealants, adhesives or glues are generally derived from blood clotting components such as proteins (e.g., fibrinogen or fibrin), enzymes (e.g., thrombin) and/or platelets. Fibrin based sealants, adhesives or glues generally combine the protein fibrinogen with the enzyme thrombin to immediately begin the clotting process. One surgical adhesive currently being marketed includes a combination of collagen (proteins which form fibers to support body tissues), formalin (a form of formaldehyde), resorcinol and glutaraldehyde. Some sealants, adhesives or glues may be used to control bleeding or to reinforce suture or staple lines rather than to make tissues adhere, thus functioning more as hemostatic agents than glues.
There are a number of uses for sealants, adhesives or glues such as replacement for sutures and staples in minimally invasive procedures where the surgeon has little room to maneuver or for the repair of aortic dissections, where the tissue is so thin it may be damaged by sutures. They may also be used for anastomotic sealing, in which the seal should not be absorbed or carotid patching, where a complete seal is desired.
Laser welding is another potential method for forming an anastomosis. Laser welding uses lasers such as CO2 lasers, argon lasers or Neodymium-YAG lasers, to join tissues together thermally instead of, for example, mechanically. One possible mechanism of laser welding of tissues is the thermal denaturation and coagulation of collagen fibrils in the tissue, which generally occur above 60° C. To improve the procedure, photosensitive dyes (e.g., indocyanine green) may be applied at the weld site to enhance light absorption and minimize thermal damage to the surrounding tissue. Using a dye that adsorbs light at a very specific frequency, a laser can be then used to selectively heat the dye and not the surrounding tissue. Photosensitive dyes used in laser welding procedures may or may not bind chemically to the tissue's proteins. Unlike sutures or staples, laser welding may offer a watertight seal to hold bodily fluids in, thereby preventing blood loss, infections and repeat surgeries. A further enhancement to the laser welding technique is to use a “solder”. Solders may comprise synthetic and/or biological components. For example, proteins such as albumin have been used in various solder formulations. Typical laser welding devices include one or more flexible optical fibers and solder-delivery tubes that may be snaked through small ports or through a channel in an endoscope.
Mechanical anastomotic devices include stapling devices, clipping devices, ring and pin coupling devices and suturing devices. These anastomotic devices may be automated or semi-automated. Mechanical anastomotic devices also include mechanical couplers including stents, ferrules, and/or rings. Materials used to form an anastomosis via a mechanical device and/or coupler may be biocompatible, bioabsorbable, bioactive and/or bioinert.
One-component intra-luminal mechanical anastomotic devices are generally stent-like in design. The graft and the target vessel, i.e., the aorta or coronary artery, are forced into tubular shapes by the device. In general, the application of this type of device is relatively easy. The device can be made to unfold by itself so no deformation forces are necessary at the anastomosis. In addition, angled anastomoses are possible. The device may however have a lot of foreign material exposed within the blood stream, thus increasing the risk of stenosis and thrombosis. In some cases, the device may prevent direct contact between the graft and the target vessel, thereby preventing the vessel walls from healing together. Intimal damage to both the graft and the target vessel may also occur during delivery of the device. Extra sealing methods, e.g., tissue sealants, may be needed to provide a leak-free anastomosis. In addition, the size of the device is strongly related to the size of the vessels. Therefore, a range of devices and measurement of the vessels may be needed.
Two component intra-luminal mechanical anastomotic devices require both the graft and the target vessel to be connected to their own coupling component, after which the two coupling components are connected to each other, thereby forming the complete anastomosis. Problems associated with construction of an anastomosis using a two component intra-luminal mechanical coupling device include mounting of the vessels and connection of the components. Tools for mounting the individual coupling components to each vessel and tools for connecting the coupling components together are both required.
One-component extra-luminal mechanical anastomotic devices generally require a delivery tool to position the coupling device in the recipient vessel. One component extra-luminal mechanical coupling devices generally allow direct intima-to-intima contact. In addition, this type of device will have less foreign material in the blood stream, thereby decreasing the risk of stenosis and thrombosis. For this reason, less biological testing may be required as opposed to an intra-luminal stent-like device. However, mounting of the graft to the coupling device may not be easy. Damage may occur due to everting of the graft onto the device. For example, everting of a graft onto a device may cause damage to the intimal layer. This damage may occur for two reasons: 1) solid grabbing of the vessel wall to evert an artery, thus one tip of the pair of pincers will roughly touch the intima; and, 2) eversion causes high strain (stretching), which will damage the arteries. Another problem is that skills are important for proper eversion. The surgeon has to estimate where to grab the vessel wall and how to lift it over one of the pins to obtain a symmetrical anastomosis. A specially designed mounting tool may make the step of mounting the graft onto the coupling device easier and may help to minimize damage to the graft. In addition, care must be taken to avoid compression of tissue by the coupling device since compression can cause pressure necrosis.
Two component extra-luminal mechanical anastomotic devices, like the two component intra-luminal mechanical coupling devices, require both the graft and the target vessel to be connected to their own coupling component, after which the two coupling components are connected to each other, thereby forming the complete anastomosis. Problems associated with construction of an anastomosis using a two component extra-luminal mechanical coupling device also include mounting of the vessels and connection of the components. Tools for mounting the individual coupling components to each vessel and tools for connecting the coupling components together may be required.
Hybrid anastomosis techniques combine one or more techniques, e.g., sutures or clips with glues or laser welding. A specific example of a hybrid anastomotic technique is the use of an intraluminal stent like device combined with an extraluminal application of biological glue.
One area that may create difficulties for the patient and extra expense and time for a stopped heart CABG procedure involves CPB. In a CPB procedure all the patient's blood, which normally returns to the right atrium, is diverted to a system that supplies oxygen to the blood and removes carbon dioxide from the blood and returns the blood, at sufficient pressure, into the patient's aorta for further distribution into the body. Generally such a system requires several separate components, including an oxygenator, several pumps, a reservoir, a blood temperature control system, filters as well as flow, pressure and temperature sensors.
Problems may develop during cardiopulmonary bypass due to the reaction blood has to non-endothelially lined surfaces, i.e. surfaces unlike those of a blood vessel. In particular, exposure of blood to foreign surfaces results in the activation of virtually all the humoral and cellular components of the inflammatory response, as well as some of the slower reacting specific immune responses. Other complications from cardiopulmonary bypass include loss of red blood cells and platelets due to shear stress damage. In addition, cardiopulmonary bypass requires the use of an anticoagulant, such as heparin. This may, in turn, increase the risk of hemorrhage. Finally cardiopulmonary bypass sometimes necessitates giving additional blood to the patient. The additional blood, if from a source other than the patient, may expose the patient to blood born diseases.
Due to the risks incurred during cardiopulmonary bypass, others have attempted to perform a coronary artery bypass graft procedure without cardiac arrest and cardiopulmonary bypass. For example, Trapp and Bisarya in “Placement of Coronary Artery Bypass Graft Without Pump Oxygenator”, Annals Thorac. Surg. Vol. 19, No. 1, (January 1975) pgs. 1-9, immobilized the area of the bypass graft by encircling sutures deep enough to incorporate enough muscle to suspend an area of the heart and prevent damage to the coronary artery. More recently, Fanning et al. in “Reoperative Coronary Artery Bypass Grafting Without Cardiopulmonary Bypass”, Annals Thorac. Surg. Vol. 55, (February 1993) pgs. 486-489 also reported immobilizing the area of the bypass graft with stabilization sutures.
Suction stabilization systems, such as the Medtronic Octopus® Tissue Stabilizer and Accessories (available from Medtronic, Inc., Minneapolis, Minn. USA), the current model being designated the “Octopus 4™ stabilization system”, use suction to grip and immobilize the surface of the heart. Additionally, the system allows the surgeon to manipulate the anastomosis site into better view by rotating and supporting the heart. See, also, e.g., U.S. Pat. Nos. 5,836,311; 5,927,284 and 6,015,378, and co-assigned U.S. patent application Ser. No. 09/396,047, filed Sep. 15, 1999, Ser. No. 09/559,785, filed Apr. 27, 2000, and Ser. No. 09/678,203, filed Oct. 2, 2000; and European Patent Publication No. EP 0 993 806. The Octopus™ stabilizer facilitates moving or repositioning the heart to achieve better access to areas which would otherwise be difficult to access, such as the posterior or backside of the heart.